Determination of ionization efficiency of glycated and non-glycated peptides from the N-terminal of hemoglobin beta-chain by electrospray ionization mass spectrometry.

We compared the ionization efficiency of glycated and non-glycated peptides for the HbA1c measurement method developed by Kobold et al. [Clin. Chem., 43 (1997) 1944] based on LC-ESI-MS analysis of the N-terminal peptides of the beta-chains released by cleavage of the hemoglobin with endoproteinase Glu-C. Taking half the peak area of the doubly charged ion and adding it to the area of the singly charged ion, we determined that the slope of the resulting calibration curve was nearly equal to 1, and the reproducibility of the added values was better than the values calculated by the doubly or the singly charged ion alone.